The present invention relates to apparatus for feeding fuel to a kiln and, more particularly, to a method and apparatus for feeding sludge into a rotary cement kiln.
In response to increasing concern over the disposal of waste material in a manner which does not generate pollution, attempts have been made to burn waste material as a part of a rotary kiln cement-making process. Use of refuse-derived fuel ("RDF"), having a volatile organic content, is desirable in a cement-making process in that the waste is incinerated at relatively elevated temperatures, such as 1,300.degree.-1,600.degree. C., which is sufficient to break down the toxic or hazardous constituents of the waste. Further, the combustion of waste adds heat to the cement-making process and the ash becomes part of the cement clinker.
Since industries and municipalities are willing to pay for the disposal of such waste, the overall cost of cement making is reduced by the income received from accepting waste and from the reduced dependence upon conventional fossil fuels in the cement-making process.
An example of such a process is disclosed in Watson, et al. U.S. Pat. No. 4,022,630. That patent discloses a method of incinerating municipal refuse by burning it in a pulverized condition in a rotary cement kiln by blowing the refuse, in a comminuted state, into a kiln at the same location as the conventional fuel burners. The device requires that the comminuted refuse have a heating value sufficient to enable it to be burned while entrained in an air stream in a manner similar to the burning of conventional fuel.
In order to utilize RDF and, at the same time, produce the highest quality cement clinker, it is necessary to burn the RDF as completely as possible. This requires that the RDF be comminuted into very small particles to increase the collective surface area of the RDF and promote mixing with oxygen. While this is relatively easy to accomplish with standard municipal refuse and liquid refuse, such as oil or cleaning solvents, it becomes difficult with more viscous material, such as sludge.
The Benoit, et al. U.S. Pat. No. 4,850,290 discloses an apparatus for burning sludge in a rotary kiln in which the sludge is injected into the kiln in the form of discrete fuel containers. The kiln body includes a radially-extending tube in which the sludge capsule is placed. As the tube passes the vertical, the sludge capsule is drawn by gravity downwardly into the kiln bed where it is burned. The sludge capsule itself comprises combustible material. A disadvantage with such a device is that the sludge is placed into the kiln in a large mass which does not promote burning of the sludge and also creates a relatively "cool" spot in the burning clinker. Such a cool spot may adversely affect the quality of the clinker produced by the kiln. Also, incomplete burning of the sludge may lead to the generation of carbon monoxide which subsequently is discharged to the atmosphere as an undesirable constituent.
Accordingly, there is a need for a device for burning highly viscous sludge in which the sludge is injected into a cement kiln in a fashion which promotes the rapid and complete burning of the sludge without affecting the quality of the cement clinker produced.